<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>

  <style>
    .container{
      width: 100%;
      height: 100vh;
    }

    .box{
      width: 100px;
      height: 100px;
      background: red;
      margin: auto auto;
    }

  </style>

</head>
<body>
  <div class="container">

    <div class="box"></div>

  </div>
</body>
</html>